Frequent contamination of edible freshwater fish with colistin-resistant Escherichia coli harbouring the plasmid-mediated mcr-1 gene

The threat of antimicrobial resistance is increasing. Microbial food contamination poses a serious public health risk; however, there are only a few studies on the prevalence of colistin-resistant Escherichia coli (COL-E) contamination in freshwater fish. This study aimed to characterise the antibiotic resistance genes and antibiotic susceptibility profiles of COL-E in freshwater fish in Vietnam. In total, 103 fish were collected and 63 COL-E were isolated. COL-E was investigated by genotyping mcr and AmpC/extended-spectrum 8-lactamase (ESBL)-related genes. The results show that COL-E and AmpC/ESBL-producing COL-E were confirmed in 24.3 % and 14.6 % of the fish, respectively. Multiplex PCR for mcr-1-9 showed that all 63 COL-E harboured mcr-1, while mcr-3 was detected in 7.9 % of COL-E. The minimum inhibitory concentration of colistin ranged from 2 to 256 mu g/mL. Meanwhile, antibiotic susceptibility results show that all COL-E were resistant to ampicillin, streptomycin, and chloramphenicol.